A101146 Indices of primes in sequence defined by A(0) = 79, A(n) = 10*A(n-1) - 31 for n > 0.

0, 2, 236, 242, 350, 966, 1842, 7404, 9632, 59820

Offset

1,2

Comments

Numbers n such that (680*10^n + 31)/9 is prime.

Numbers n such that digit 7 followed by n >= 0 occurrences of digit 5 followed by digit 9 is prime.

Numbers corresponding to terms <= 966 are certified primes.

a(11) > 10^5. - Robert Price, Oct 03 2015

References

Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.

Links

Table of n, a(n) for n=1..10.

Makoto Kamada, Prime numbers of the form 755...559.

Index entries for primes involving repunits.

Formula

a(n) = A103062(n+1) - 1.

Example

79 is prime, hence 0 is a term.

Mathematica

Select[Range[0, 100000], PrimeQ[(680*10^# + 31)/9] &] (* Robert Price, Oct 03 2015 *)

Prog

(PARI) a=79; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-31)
(PARI) for(n=0, 1000, if(isprime((680*10^n+31)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A103062.

Sequence in context: A057157 A139963 A124046 * A159280 A013477 A013473

Adjacent sequences: A101143 A101144 A101145 * A101147 A101148 A101149

Keyword

nonn,hard,more

Author

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 03 2004

Extensions

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008

a(10) from Robert Price, Oct 03 2015

Status

approved